Add solutions for searching in 2D matrix (LeetCode #74 and #240)

src/main/java/com/thealgorithms/matrix/Search2DMatrix.java

@@ -0,0 +1,83 @@
+package com.thealgorithms.matrix;
+
+/**
+ * Two variations of searching in a 2D matrix
+ *
+ * Variation 1:
+ * - Each row is sorted left to right
+ * - Each column is sorted top to bottom
+ *
+ * Variation 2:
+ * - The matrix is a flattened sorted array
+ * - i.e., row 0 ends, row 1 continues (matrix is sorted as a 1D array)
+ *
+ * LeetCode: #74 and #240
+ */
+public class Search2DMatrix {
+
+    /**
+     * Search in a 2D matrix where rows and columns are sorted.
+     *
+     * @param matrix The 2D matrix with sorted rows and columns.
+     * @param target The target integer to search for.
+     * @return true if target is found, otherwise false.
+     */
+    public static boolean searchMatrixSortedRowsAndCols(int[][] matrix, int target) {
+        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
+            return false;
+        }
+
+        int rows = matrix.length;
+        int cols = matrix[0].length;
+
+        int row = 0;
+        int col = cols - 1;
+
+        while (row < rows && col >= 0) {
+            int val = matrix[row][col];
+            if (val == target) {
+                return true;
+            } else if (val > target) {
+                col--;
+            } else {
+                row++;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * Search in a 2D matrix that is sorted as if flattened into a 1D array.
+     *
+     * @param matrix The 2D matrix.
+     * @param target The target integer to search for.
+     * @return true if target is found, otherwise false.
+     */
+    public static boolean searchMatrixFlattenedSorted(int[][] matrix, int target) {
+        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
+            return false;
+        }
+
+        int rows = matrix.length;
+        int cols = matrix[0].length;
+
+        int left = 0;
+        int right = rows * cols - 1;
+
+        while (left <= right) {
+            int mid = left + (right - left) / 2;
+            int val = matrix[mid / cols][mid % cols];
+
+            if (val == target) {
+                return true;
+            } else if (val < target) {
+                left = mid + 1;
+            } else {
+                right = mid - 1;
+            }
+        }
+
+        return false;
+    }
+}

src/test/java/com/thealgorithms/matrix/Search2DMatrixTest.java

@@ -0,0 +1,30 @@
+package com.thealgorithms.matrix;
+
+import static org.junit.jupiter.api.Assertions.*;
+import org.junit.jupiter.api.Test;
+
+public class Search2DMatrixTest {
+
+    @Test
+    public void testSearchMatrixSortedRowsAndCols() {
+        int[][] matrix = {
+            {1, 4, 7, 11},
+            {2, 5, 8, 12},
+            {3, 6, 9, 16},
+            {10, 13, 14, 17}
+        };
+        assertTrue(Search2DMatrix.searchMatrixSortedRowsAndCols(matrix, 5));
+        assertFalse(Search2DMatrix.searchMatrixSortedRowsAndCols(matrix, 20));
+    }
+
+    @Test
+    public void testSearchMatrixFlattenedSorted() {
+        int[][] matrix = {
+            {1, 3, 5, 7},
+            {10, 11, 16, 20},
+            {23, 30, 34, 50}
+        };
+        assertTrue(Search2DMatrix.searchMatrixFlattenedSorted(matrix, 3));
+        assertFalse(Search2DMatrix.searchMatrixFlattenedSorted(matrix, 4));
+    }
+}